Acid recovery process



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. *IZ JIITII 'I7 g l I Y le 40 HJ GaSAHcad u April 10, 1945 MQvooGD ETAL A 2,373,359

ACID RECOVERY PROCESS Filed Maren 8, 1943 Wash Towzr F'QJII lnvzni'orsrFrank E.Caddq. Charkzs H.- Duffg Maar-ien Voogd YM *hdr AHOVMLJLL M it has been tonnel that theo a,

Patented Aprrl,

UNITED STAT its 4PnisN'r 2,373,359

, ACID RECOVERY PROCESS Maarten Voogd, lione` Beach, Frank E. Caddy, l

Compton, ,and Charles H. Daily, Long Beach, Calin.,o asslrnors to Shell Development Compatib- Son Francisco, Calif., a corporation cl2 Delaw application Maren s, ms, semi No. 478,452

(ci. ca -172) manufacture of alcohols, ethers, and the like from olens as descri. for example, in U. S. Patents 1,912,695, 2,060,143 and 2,0S8,083.

When alcohols `are manufactured by absorbing cone or more olens in sulfuric-acid, usually of about 85 to 100% concentration, and diluting and acid in a condition suitable for reinorganic impurities may lie accomplished by ,the introduction of nitric acid into one ofthe concentrating stages which contains 1 l' n c acid at an optimum concentration for such treatment.

Further concentration ofthe acid to a st l l suitable for re-use in the alcohol manui'ac process may be carried out in a vacuum conl centrator.

An important object of the invention is the`provision of a method for reconcentrating spent acid wherein the carbonization and separation or4 orgenie impurities are reduced to a --w f-ff:: and the vaporization ofsuch impurities increased to a maximum. A further object is to' provide a is method and apparatus wherein la spent acid y e@ vantages to be derived from' operating ezt-f hydralazine the resulting alkyl sulfates, a stripped acid liquor is obtained after removal ci the alcohol or alcohols, 'which acid liquor is generally too dilute to ce directlyreturned to the processior absorption 'of :more olen.

Due to the presence 'of organic 'impurities in theacid liquor. it .i .4 ne continuously reconcentreted and refused after concentration in a vacuum concentrator as the carbon content of the acid gradually increases to auch en extent that the presence of the impurities seriy interre with the delicate control nece :1' i in the alcohol process. n still more important objection to tnepresence of such carnonaceous impurities in reaction systemresides 'in the fact that' the presence of such material causes the following detailed description thereof,

, wnicniorm a, l 25 E preferred am] .nl

active decomnon o the :wi-` c acid inthe acid concentrators, not if destro@ a substantial emountof? this ressent, but pacing substaniiel volumes oi sulfur dioxide sas which must ne eliminated, Acco to thepresent lnventi chew *acid may separated d removed heating under particular conditions and. when followed by nrther heating undery 'vacuuml condi tions, acid only suitable for reause in an nlcohl :ritmously obtained.

i The process of time present invention comprises .essentially nesting the acid liquor in several separate stages by se e tel?l generated hot combustion gases whereby a srauai concentration of process/can he continu` ne easily and economically purined and reooncen trated in a plurality of stag, with me 1.,"

neiiibility of control providedl for each stage.

Other objects, together with some of the adto the present invention, t .lo aent in reference also beine ci to the om 0f this Bp oi 1the invention Referring to the drawing: We I is a longi-l tudinal' section or oneo n of the'primary concentrator apparatus; Figure His end elevation through H-H of @le I; ure is a sche--v matic now sheet oi the procesa incorporating the primary concentrant apratus yshown 'in- Figures andiil. l

Referring ifiarticnlarly` to ratus comprises a horizontal steel for... i (hereinafter called' the primary concentrator) divided into 4 chersia, ib, ic d icl. villie' :i is provided with a lead 1i: f f: li and also with a g' of acid resistant brick t within said leed .i I 'w in order to providel further protection for the mtal. The partition walls t, 't enlist separate the tank A into the d chambers. The acid may be delivered w c impurities in the acid takes place. and concomltantly a-graduai setion and vaporization oi' the organic im.

purities. al removal of low concentrations 55M to cliber la .by means of pim l. From cham lierl ia the acid llotvs to chamber lo by an overnow pipe t, in ition t, thence to chamber ic by. means of overflow pipe Q in partition t', thence to chamberl id by meansof overnow pipe i@ in partition 3. The acid is withdrawn from chamber t throughplpe il.A

In each. of the 1 chambers iat, ib, ic and id is,

.dlsd asubxnerged combustion burner corn-l pli-lainer a dip-pi it extending from the top of the chamber cloivniirdv so as lto be immersed in the liquid for appro u tely one foot, or as much 'lesa or more as proves practical for a substantially complete exce oi' heatj frorn -gas `to liquid oFF-ics i n l, the appie@ l other.

without causing an excessive liquid spray. For the last reason the lower end is serrated at IB, which aids in more effectively distributing the ehot combustion products through the acid body. Within dip-pipe I is provided a gas-air mixture feed pipe I3 which terminates at its lower end in a dispersion cup I4 winch is in turn provided with a perforated burner plate asat I1. A combustible gas-air .mixture is supplied to feed pipe I3 from mixer I2.

Partition wall 5 reaches to the roof of the tank I in such a manner as to divide the vapor space of the tank into two parts, chambers Ia and Ib 23 leaves the top ofthe tower and discharges intoV a stack (not shown). An oxidizing agent may be passed into chamber Ic through conduit 3|.

Figure l1 illustrates the details of the submerged combustion burner which comprises a mixing chamber I2 into which 'an air conduit 25 and a gas conduit 26 discharge. Regulating valves 21 and 28 serve to control the ratio of air to gas supplied to ',feed pipe I3.

Referring to Figure III, spent acid having a concentration' of about 45% by weight HzSOi from a reactor 29 is passed through conduit -1 to l primary `concentrator I.

Acid leaving primary concentrator I through conduit II will have a concentration of approximately H2504. This acid may either be passed through a filter unit 32 whereby separated carbonaceous materials remaining are removed; or/alternatively, if the acid impurities are of such nature that they are substantially all vaporized in primary concen- -tratori acid maybe passed directly through conduits II 33 land 34 to a 4vacuum concentrator 35. After concentration under vacuum to any desired point, usually to approximately 85%. mSOa for re-use in olefin absorption, the purified, reconcentrated acid is passed through conduit 36 and returned to reactor 29.

Referring again to Figure I, dilute, contaminated acid is continuously passed through conduit 1 and into the body of acid maintained in -it can most economically be further concentrated by means of a vacuum unidas described above in connection with Figure III.

In the methods at present used for reconcentratng spent sulfuric acid, i. e., heating the spent acid either indirectly by means of steam coils or the like, or passing hot :due gases through .the

spent acid.conside`rable difliculty is had due to the formation and separation of carbonaceous material of such nature as to be extremely dinicult to iilter. According to the present invention it has been found that most of the impurities present in spent lacid which has been used in absorbing olens and similar processes are normally of such nature as to volatilize Without substantial formation of precipitated carbcnaceous material. However, the prolonged heating of the feed acid in an acid bath of considerable concentration and temperature tends to bring vabout the polymerization of the volatile impurities to form polymers which carbonize and separate from the acid as a precipitate or a diilicultly filterable suspension, necessitating inturn the usecf complicated and expensive filtering equipment.

or less fiash'or (sudden) volatilization of the organic impurities odcurs in each stage before substantial polymerization. Thus, the major portionof the organic contaminants' in the spent acid is vaporized and removed through the vapor outlet along with the Water vapor and combustion products from the submerged burners.

g as shown in Figure I. In this manner, separated chamber.' la. A combustible gas mixture, usually air and methane,` although any suitable combusi tible vmixture which will yield combustion products having a temperature preferably of the order of 2800? F.' may beutilized,l is supplied to the sube merged combustion burner. The combustion of the air-gas mixture is carried out continuously As a result of theintimate contact between the y dilute acid and thecombustion products from the submerged burner, extremely lidcient heat transfer is obtained,`as evidenced' by the fact that the temperature of the vapors exiting through conduit I1is of the order of 200 F.

' The dilute acid in passing successively throughV chambers Ia,` Ib, Ic and Id is gradually concentrated to approximately 70% H2804, after which It will be found, however, that some types of spent acid contain relatively large quantities of higher boiling organic contaminants which are dimcult to vapcrize even when submerged combustion burners are utilized. In such instances, concentrated nitric acid or other suitable strong oxidizing agents may be added to the third stage of the'primary concentrator through conduit 3|,

carbonaceous materialpassing'into chamber Ic is oxidized to formcarbon dioxide which passes overhead through conduit I8. An oxidizing agentv should be utilized which will itself vaporize at a point not exceeding the boiling temperature of approximately '10% H2804, i. e., about 165 C. For this reason, nitric acid is preferably used for this purpose since anyexcess of nitric acid passing into chamber. Id will be .vaporized and pass overhead through conduit It.O When reconcen'-v trating sulfuric acid which has been utilized in absorbing olens, it has been foundthat approximately 1%- by weight of concentrated nitric and autresV to thethird stage 'of/.the primary concentrator 'is suflicient to oxidize the major portion of any non-vaporizable organic materials entering the thlrdstagc. It is preferable when utilizing nitric acid as anV oxidizing agent to adjust the submerged combustionA burners of the various stages in a manner to ensure that the nitricacid is' added in the stage preceding' the stage in which a Aconcentration of '70% is maintained. The reason for this is, that while the oxidation with nitric acid is-satisfactory between wide limits of sulphuric acid concentration, the

ture of water vapor, carbon dioxide, nitrogen -and small amounts of SO2 and S03. This gas mix ture is washedl in spray tower with a countercurrent water stream before being released to the-atmosphere through conduit 23. Depending on availability of water, this water can be passed to the sewer through conduit or, after cooling,

' in a cascade cooler recirculated through the conf densing tower. In the latter 'case, the solution will be rendered acid by the small amount of The vapor -leaving primary concentrator i through'conduit I9 comprises essentially a mix- We claim as our invention:

1.l In amethod of. concentrating acid vcontaining organic ncontaminants derived from olen absorption processes, the steps comprising maintaining a plurality of separate bodies of acid of progressively increasing concentrations,

passing. said dilute acid to the first of sa'id bodies of acid, withdrawing concentrated acid from the last ifv said bodies of acid, successively passing acidic vapors being absorbed in the water and a small amount of acid spray being precipitated.

It'is preferable, according to the present invention to carry out the concentration in the primary concentrator in several stages, as shown v in Figure I, as in this manner the introduction of a relatively weak acid into a relatively strong,.

boiling acid may be avoided and the subsequent formation of non-volatile polymers from volatile organic contaminants further obviated.

It has been found' that in most instances recovered, reconcentrated acids may be re-used for olefin absorption with results equivalent to the use of fresh acid if the organic contaminant content of the recovered acid is maintained at approximately 0.1% by weight or less. Accordingl to the present process the organic contaminant content of spent acids containing even as much as .0.5% by weight of organic contaminant may be easily reduced to the order of 0.1% or less'without modification of the process as described above.V For example, a spent acid having a concentration.

of 47.0% HQSO@ and containing ,0.43% by weight organic' contaminants was processed in the manner described above. The concentration was raised to 68.5% H1804 in the primary concentrator and .thereafter further concentrated to 85.0% HiSOil in a vacuum .concentrator vof the -Mantius type. The reconcentratedacid upon analysis con.

tained 0.07% by weight of organic contaminants.

zio

acid from each o f said bodies of acid to the body of acid of next highest concentration and subjecting each of said bodies of acidv to the action of a continuous stream of combustion gases produced by the action o f submerged combustion burners beneath the surface ofthe acid whereby a maximum portion of said organic contaminants is` suddenly volatilized. j y

2. In a method of' concentrating dilute sulfuric acid containing organic contaminants derived from olen absorption processes, the steps comprising maintaining a pluralitybf separate bodies of acid of progressively increasing concentrations, continuously passing said dilute acid to the rst of said bodies of acid, continuously withdrawing concentrated acid from the last of said bodies of acid, continuously passing acid from each of said bodies of acid to the body of acid of next highest l `acid containing organic contaminants derived from olen absorption processes, the steps comprising maintaining a plurality of separate bodies of acid of progressively increasing concentrations, continuously passing said dilute acid to the rst -ofsaid bodies of acid, continuously withdrawing The acid in the 'third stage of the primary concentrator was'treated .with 0.8% by volume of concentrated nitric acid.

The number of stages which may be most eiiicaciously utilized inl the primary concentrator will of course vary with particular acids, consideration being-given to'the spent liquor concentration and organic -impurity content of the ,acid

concentrated acid from the last of said bodies of acid, continuously passing acid frcm'eachof said bodies of acid to the body of acid of next highest concentration and continuously generating a stream of combustion gases having a temperature of the order of 2800 F. beneath the surface of each of said bodies of acid whereby a maximum to be recovered. AAs has been mentioned before,

the optimum concentrationto which an acid may be reconcentrated by means of submerged com.

bustion burners is of the order of approximately4 70%; higher concentrationsmay be attained, although in view of 'the'relatively large quantities of S03 evolved in, passing hot combustion gasesthrough sulphuric' acido: high concentration, the economy of theprocess has to be restored by precipitation and recovery. of this acidI component. This, in generali may most satisfactorily it is preferable vluotlio attempt to vincrease the concentration of adilpie acid more than approxi'- mately 10% on thev ,average in eachfstage, from .5% to 10% onthe average in each stagebeing the preferred range. It is to be emphasiaeilhowever,

f that in thoseinstallations wherein nitric acidis to .be added tothe primary concentrator a body of acid Should be maintained me having a 'concentrationof atzle'ast'approximat'ely 80% =byv'welgm; and not substantially exceeding '10% be done by electrostatic precipitation. In general,

y'portion'o'f said organic contaminants is suddenly l volatilized.

.- 4. In a method of concentrating dilute sulfuric A acid containing organic 'contaminants derived from olen absorption processes, the steps `corne prising maintaining a plurality of separate bodies of acid of progressively increasing concentration,

continuouslypassing said dilute acid to the ilrst of said bodies of acid, continuously withdrawing concentrated acid from the last of said bodies of` acid, continuously passing acid from each of said bodies of acid to the body of acid of next highest concentration, continuously subjecting each of said bodies of acid to the action of a continuous stream ofcombustion gases produced by the ac- L tion vof submergedcombustlon burners beneath 'the surface of the acid whereby va. maximum por- 4tion of said organic contaminants is volatilized and subjecting remaining organic contaminants by weight; preferably within the ap oximate .'rangecrssat byweignttozoaby t.'

to the action of a strong oxidizing agent whereby they are suddenly volatilize'd.-

acid containing organic contaminants derived from .olefin absorption processes,the steps comprising maintaining a plurality of separate bodies 'of acid of progressively increasingconcentrations, continuously said dilute acid tothe vfirst dilute sulfuric 75. In a method of concentrating dilute concentrated acid from the last of said bodies of acid, continuously passing acid from each of said bodies of acid to the body of acid of next highest concentration, maintaining the concentration of one of said bodies of acid Within the approximate range of 60% to 70% by weight of H2804, subjecting each of said bodies of acid to the action of a continuous stream of combustion gases produced bythe action Of--submerged combustion 10 range of 60% to 70% by weight of H2504, subburners beneath .the surface of the acid whereby a maximum portion of said organic contaminants Y is suddenly volatiiized and continuously adding a g .volatile oxidizing agent to said body of acid maintained within the approximate rangeof 60% to 15 '70% by weight H2SO4 whereby a maximum portion of the remaining organic contaminants is suddenly voiatilized.

6 The method according to claim 5 wherein the acid bodyto which the oxidizing agent'is 20 added is maintained-at a concentration Within the approximate range of 65% to '70%,by weight of. acid, the concentration of the .acid in said 30 bodies increasing progressively by increments of asvaaso approximately 5% .to 10% by weight of H2804, continuously passing said dilute acid to the acid body having the lowest acid concentration, continuously withdrawing acid having a concentration of approximately 70% by weight HzSO4 from the acid body having the highest concentration, continuously passing acid from each of said ,bodies of acid to the body of acid of next highest concentration, maintaining the concentration of one of said bodies of acid within the approximate jecting each of said bodies ofv acid to the action of a continuous stream of combustion gasespr duced by the'action of submerged combustion burners beneath the surface of the -acid whereby a maximum portion of said organic contaminants is suddenly volatilized and continuously adding concentrated nitric acid to said body of `acid maintained at a concentration within the approximate rangeof 60% to 70% by Weight H2804 whereby a maximum portion of the remaining organic contaminants is sudeniy voiatilized. 9. The method according to claim 8 wherein the quantities of nitric acid vadded amount to approximately 1% by volume of the acid owing through the acid body wherein the nitric acid is added.

MAA'RTEN vooGD. FRANK E. CADDY. CHARLES H. DUFFY. 

